Analytica Chimica Acta 808 (2014) 3–9

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Review

Tandem mass spectrometry of low solubility polyamides Caroline Barrère a , Marie Hubert-Roux a , Carlos Afonso a , Majed Rejaibi b , Nasreddine Kebir b , Nicolas Désilles b , Laurence Lecamp b , Fabrice Burel b , Corinne Loutelier-Bourhis a,∗ a b

Normandie Université, COBRA, UMR 6014 et FR 3038, Université de Rouen, INSA de Rouen, CNRS, 1 rue Tesnière, 76821 Mont Saint Aignan Cedex, France Normandie Université, INSA de Rouen, CNRS UMR 6270 PBS & FR 3038, Avenue de l’Université, 76801 St Etienne du Rouvray, France

h i g h l i g h t s

g r a p h i c a l

a b s t r a c t

• MALDI-TOF/MS-MS

studies of polyamides. • Orientation of fragmentation processes by end group derivatization. • Fragmentation rules.

a r t i c l e

i n f o

Article history: Received 23 January 2013 Received in revised form 25 March 2013 Accepted 29 March 2013 Available online 8 April 2013 Keywords: MALDI-MS/MS Polyamides Fragmentation rules Derivatization

a b s t r a c t The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. Because of interferences for precursor ions selection, two chemical modifications of the polymer end groups were proposed as derivatization strategies. The first approach, based on the addition of a trifluoroacetic acid (TFA) molecule, yields principally to complementary bn and yn product ions. This fragmentation types, analogous to those obtained with peptides or other PA, give only poor characterization of polymer end-groups [1]. A second approach, based on the addition of a basic diethylamine (DEA), permits to fix the charge and favorably direct the fragmentation. In this case, bn ions were not observed. The full characterization of ␻ end group structure was obtained, in addition to the expected yn and consecutive fragment ions. © 2013 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Chemical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Polymer synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Chemical modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. MS/MS study of Polymer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. MS/MS study of Polymers 2 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

∗ Corresponding author. Tel.: +33 2 35 52 29 24; fax: +33 2 35 52 24 41. E-mail address: [email protected] (C. Loutelier-Bourhis). 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.03.064

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Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Polyamides (PA) constitute an important class of polymer. They are very attractive because of their good chemical resistance, high thermal stability and good mechanical properties that offer a wide range of applications in medicine, textile and car manufacturing industry. Moreover, the interest to extend the application fields of such materials leads to the development of new types of PA, in particular from renewable resources [2–5]. In this context, the structural characterization of original PA is essential to establish structure properties relationship. PA characterization studies have been reported by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS), widely used as an efficient method to analyze synthetic polymers [6–9]. Montaudo et al. have reported Nylon 6 (Mw = 43 000 Da) analysis after sample hydrolysis with aqueous methanesulfonic acid to decrease the polymer molecular weight [10]. Choi et al. have also reported Nylon 6 and Nylon 6,6 characterization with the same strategy [11]. Other works have shown the characterization of new polyamides by MALDI-TOF-MS [12,13]. In order to facilitate Nylon 6,6 analysis, Weidner et al. have developed semi on-line coupling of liquid chromatography at critical conditions and MALDI-TOF-MS [14]. All these studies have shown that the main difficulty to analyze PA is related to their low solubility. As an alternative to these solvent-based analyses, solvent-free approaches was developed by Skelton et al. to facilitate low soluble PA analysis by MALDI-TOF-MS [15]. Therefore, solvent-free strategy in MALDI sample preparation has a growing interest with the development of the well-known “solvent-free” [16] or “evaporation grinding” methods [17]. A recent study from our group focused on the optimization of MALDI experimental conditions, where solvent-free with different solvent-based approaches for PA11 analysis were compared [18]. This study showed the presence of cyclic oligomers by-products, formed during the polymerization step, which were detected along the expected linear species. Such results were also reported for Nylon 6 in a previous paper of Montaudo [10]. Regrettably, the signals of both cyclic and linear polymers were overlapped preventing precursor selection of a unique species for tandem mass spectrometry experiments (MS/MS). MS/MS data can afford relevant structural information on polymer chain and end-groups. To overcome such interference situation, we performed the chemical modification of the vinylic end-groups of the linear polymer with trifluoroacetic acid (TFA). Such derivation permitted to separate unmodified cyclic from modified linear species in the mass spectrum, and allowed to perform MS/MS experiments. However, only few fragmentation studies have been reported for polyamides in the literature, probably due to the difficulty to analyze these compounds. Yuan et al. have characterized soluble PA, based on N-methylpyrrole and N-methylimidazole, in methanolic solution by electrospray ionization tandem mass spectrometry [19]. Fournier et al. have studied the fragmentation of several protonated nylons (PA6 and PA12) presenting different end-groups by post-source decay (PSD) with a MALDI-TOF-MS instrument [1]. They observed fragmentation pathways similar to those of peptides involving bn , yn and zn ions according to the Roepstorff–Biemann nomenclature [20]. In this study, we propose two derivatization strategies involving chemical modification of either the initiating (␣) or terminating (␻) end-groups of linear PA11 to allow MS/MS experiments. The fragmentations of the resulting polymers will be studied and

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dissociation rules established. Moreover, a comparative study of the different derivatized polymers (showing different end-groups) would permit to understand the influence of PA11 end-groups on fragmentation pathways. 2. Experimental 2.1. Chemical 11-Aminoundecanoic acid (CAS no. 2432-99-7), 10-undecenoic acid used as chain limiter (CAS no. 112-38-9), trifluoroacetic acid (reagent plus 99%), N,N-diethyl propanediamine (DEPDA) (CAS no. 104-78-9) and 2,5-dihydroxybenzoic acid (2,5-DHB) were purchased from Sigma Aldrich (St. Louis, MO). Sodium iodide (Ultrapure) was from Prolabo (Vitry sur Seine, France). 2.2. Polymer synthesis 500 mg of 11-aminoundecanoic acid and 25.4 mg of 10undecenoic acid as chain limiter were introduced in a 50 mL two-necked flask fitted with a magnetic stirrer, a Dean–Stark topped by a condenser, and a switchable inlet for nitrogen. A molar ratio of 1:18 between chain limiter and monomers was used. The reaction mixture was placed under nitrogen flow for 20 min before the two-necked flask was immersed in an oil bath at 220 ◦ C. After melting of the reactants, the mixture was stirred magnetically for 2 h 30 min. The reaction took place under stream of nitrogen. At the end of the reaction, the synthesized product was allowed to cool completely at room temperature for at least 1 h under a nitrogen purge. The resulting polymer was recovered by cooling with liquid nitrogen to obtain a solid polymer which was broken in pieces and crushed into a white powder. 2.3. Chemical modification TFA modification was performed dissolving the polymer (5 mg mL−1 ) in neat TFA. The mixture was stirred under magnetic agitation at room temperature for 4 h. Diamine modification was carried out using a three-necked flask fitted with a magnetic stirrer, a Dean–Stark topped by a condenser. A solution of initial polymer (490 mg) in dimethyl sulfoxide (10 mL) was added to 20 mL of N,N diethyl-1,3-propanediamine. The mixture was heated to 190 ◦ C under magnetic stirring during 3 h. Then the mixture was cooled to ambient temperature and the modified polymer was filtered under vacuum conditions and dried in an oven during 2 h under vacuum conditions. 2.4. Mass spectrometry MALDI-TOF-MS and MALDI-TOF/TOF-MS experiments were performed on an Autoflex III time-of-flight mass spectrometer (Bruker Daltonics, Bremen, Germany) equipped with a frequencytripled Nd:YAG laser emitting at 355 nm. FlexControl (3.3) and FlexAnalysis (3.3) software package (Bruker Daltonics, Bremen, Germany) were used for data acquisition and processing. Spectra were acquired in the positive-ion reflectron mode at 50 Hz laser shot frequency. The acceleration voltage was set to 19 kV and the extraction delay time used was set to 220 ns in MS mode. Samples were prepared using the thin-layer method by spotting successively 1 ␮L of 2,5-DHB as matrix (10 mg mL−1 in methanol)

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Fig. 1. MALDI-TOF-MS spectra of PA11 recorded on a sample solubilized in TFA at (a) t = 0 (no derivatization) and (b) t = 4 h (derivatization with TFA). (c) MALDI-TOF-MS spectrum of PA11 modified with N,N-diethyl propanediamine.

and 1 ␮L of polymer (5 mg mL−1 in TFA) on the target plate. Samples were deposited on the MTP 384 target plate. The recorded mass spectra were the result of 1500 individual spectra averaged. The laser fluence was set slightly higher than matrix desorption threshold (∼55% of maximum laser fluence). External calibration of MALDI-TOF mass spectrometer was carried out using a mixture of poly(propylene glycol)s. For product ion analysis in the tandem time-of-flight (TOF/TOF) mode, the recorded mass spectra were the result of 1000 individual spectra averaged in the parent mode (55% of maximum laser fluence) and 4000 spectra averaged in the fragment mode (75% of maximum laser fluence) for protonated adducts. The precursor ion kinetic energy was 8 keV. The ion selection was carried out with a time ion gate with a selection window of ±6 m/z unit. Product ions generated by laser induced dissociation were further accelerated to 19 keV in the Bruker LIFT cell that allows a full product ion spectrum to be recorded. 3. Results and discussion Fig. 1 shows the MALDI-TOF-MS spectra obtained for the PA11 (a) solubilized in TFA and directly analyzed (t = 0 h), (b) after incubation in TFA for 4 h (t = 4 h) and (c) after derivatization with (DEPDA), respectively. The mass spectrum of PA11 recorded immediately after solubilization in TFA (Fig. 1(a), no modification expected) displays three different main distributions with a mass difference of 183.3 m/z unit between two consecutive ions which corresponded to the expected repeat unit A11 (i.e. mA11calculated = 183.2 Da) [9]. The three distributions corresponded to protonated molecules [PA11n +H]+ , sodium [PA11n +Na]+ () and potassium [PA11n +K]+ adducts, respectively (with n corresponding to the number of repeating unit). The experimental sum of end group weights, (m␣ + m␻ )experimental = 184.0 Da, was consistent with the calcutated value, (m␣ + m␻ )calculated = 184.1 Da, confirming the expected chainends of unmodified PA11. In addition to these ions, protonated and sodiated cyclic species (Scheme 1(b)) were also detected at 1 m/z unit down-shifted relative to the linear species, as previously reported [18]. Note that the possible by-product corresponding to non-undecenoic acid N-terminated PA11 was not detected in this sample; this by-product was not formed during the polymerization process, as previously verified by UHPLC/ESI-TOF-MS accurate mass measurement [18]. Fig. 1(b) shows the sodiated underivatized oligomers [PA11n +Na]+ () as well as additional distributions mass shifted by 114.0 m/z unit which could be attributed to protonated molecules [P1n +H]+ , sodium [P1n +Na]+ (䊉) and low intensity potassium

adducts [P1n +K]+ of TFA-derivatized PA11, referred as Polymer 1. According to our previous study, Polymer 1 resulted from the addition of TFA on the terminal double bond (Scheme 1(c)) [18]. This reaction is the result of a hydrogen transfer from the acid to the double bond with the formation of a carbocation which then reacts with the trifluoroacetate anion [21]. The determined sum of end group weights ((m␣ + m␻ )experimental = 298.0 Da) was consistent with the calculated value of 298.1 Da. The spectrum of Fig. 1(c) obtained for polymer sample after derivatization with N,N diethyl-1,3-propanediamine (DEPDA) displays four intense distributions. Two of them corresponded respectively to protonated molecules [P2n +H]+ and sodiated adducts [P2n +Na]+ of DEPDA condensation products, labeled as Polymer 2 (). The derivatization reaction involved amidification reaction between the primary amino group of DEPDA and the carboxylic acid end-group of linear PA11 (Scheme 1(d)). This was confirmed by the sum of end group weights, m␣ + m␻ = 296.4 Da in both cases ((m␣ + m␻ )calculated = 296.3 Da). The latest distributions correspond to protonated and sodiated () adducts of unexpected species referred as Polymer 3 for which the sum of end-group molecular weight were of 130.3 Da ((m␣ + m␻ )calculated = 130.3 Da). Based on the sum of end groups, Polymer 3 could correspond to both -H and -DEPDA terminated polymer (Scheme 1(e)). This species was not expected because, as previously mentioned, the nonundecenoic acid N-terminated PA11, which could lead to Polymer 3 after DEPDA derivatization, was not detected for the underivatized sample (Fig. 1(a)). Besides, the assumption that these unexpected ions series arised from ions of Polymer 2 by in source decay (ISD) with the neutral loss of the chain limiter moiety could not be retained since such ISD dissociation was not observed in the case of PA11. Consequently, this polymer was probably formed during the derivatization step either by elimination of the chain limiter moiety of linear species or by addition of DEPDA on cyclic species. The three differently terminated Polymers 1, 2 and 3 were then submitted to MALDI-TOF/TOF-MS experiments to study their fragmentation pathways and to determine potential rules for interpretation of tandem mass spectra of such compounds. Protonated molecules were selected as precursor ions. Note that product ions were labeled using a combination of the nomenclature recently proposed by Wesdemiotis for polymers fragmentation [9] and the nomenclature for peptide fragmentation, because of the presence of amide bond in PA [20,22]. Briefly, the nomenclature we proposed defines the chain limiter/N-terminal group as the initiating (␣) chain end and C-terminal group as terminating (␻) chain end to be consistent with the peptide nomenclature (because PA11 was synthesized by polycondensation). The product ions containing the

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Scheme 1. Molecular structures of (a) linear and (b) cyclic PA11, (c) Polymer 1, (d) Polymer 2 and (e) Polymer 3.

initiating end group are named with letters from the beginning of the alphabet (a, b and c), while products ions containing the ␻ terminating end group are named with letter from the end of the alphabet (x, y and z). The product ions which lose both end groups are named by a letter in the middle of alphabet or with an explicit notation for characteristic losses. In the case of PA, the main fragmentation pathways that we expect should involve the amide bond, similarly to peptide fragmentation. Additional details can be found in the Wesdemiotis paper [9]. The MALDI-TOF/TOF-MS study of Polymer 1 exhibiting Nterminal TFA-derivatization is first presented. Then, the gathered MALDI-TOF/TOF-MS studies of both Polymers 2 and 3 are presented since they were both DEPDA-derivatized onto the C-terminal chain end. 3.1. MS/MS study of Polymer 1 Fig. 2 shows the MALDI-TOF/TOF-MS spectrum obtained for the protonated 3-mer [P13 +H]+ precursor ion at m/z 848.6 (oligomer containing 3 repeat units).

One of the main fragmentation processes for m/z 848.6 involved the neutral loss of a TFA molecule yielding the abundant product ion at m/z 734.8 (Scheme 2). Other dissociation processes could involve amide bond cleavage from either m/z 734.8 or m/z 848.6 ions. When the charge was retained onto the C-terminal chain end, y3  , y2  and y1  ion series were detected at m/z 568.6, 385.4 and 202.2, respectively. The yn  product ion series permitted us to confirm the mass of ␻ end-group, while ␣ end-group can be deduced from the corresponding neutral losses. Then, competitive neutral losses of either NH3 or H2 O molecules from yn  ions yielded two other series, z3 , z2 , z1 and j3 , j2 , j1 product ions, which were detected at m/z 551.6, 368.3, 185.2 and m/z 550.5, 367.3, 184.2, respectively. The zn and jn series could further dissociate with elimination of H2 O affording the ions at m/z 533.5 (z3 -H2 O), 350.3 (z2 -H2 O), 532.5 (j3 -H2 O) and 349.3 (j2 -H2 O). The dissociation of amide bond from the precursor ion also yielded b2 and b1 product ions, which are respectively complementary to y1  and y2  ions and were detected at m/z 647.6 and 464.3 respectively. As in the case of peptides, this behavior is consistent with the formation of an intermediate proton bounded dimer that

Fig. 2. MALDI-TOF/TOF-MS spectrum of protonated [P13 +H]+ at m/z 848.6. Gray areas correspond to metastable ions.

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Scheme 2. Fragmentation pathways of protonated 3-mer [P13 +H]+ ion at m/z 848.6.

can competitively lead to the formation of a yn  or bn ion, depending on the relative proton affinity of each partner of the dimer [23]. Again, the bn fragment ion series allow the mass of ␣ end-group to be verified. Moreover, b2 and b1 product ions could lose one TFA molecule to give b2-TFA and b1-TFA ions at m/z 533.5 and 350.3, respectively. These ions could also come from the dissociation of ion at m/z 734.8. The dissociation of ␣ end-group from bn-TFA series could also explain the jn product ion series. Additional and unusual ions, referred as k3 and k2 , were detected at m/z 646.6 and 463.3. Considering that no ion was observed in the neighboring of the [P13 +H]+ ion at m/z 848. 6 on the MALDI-TOF-MS spectrum, we can suppose that this precursor ion was the sole species selected for the MALDI-TOF/TOF-MS experiment and that k3 and k2 came from consecutive fragmentation of [P13 +H]+ . Based on the sum of end groups, we suppose they came from the rearrangement of precursor ion with the migration of trifluoroacetyl group. Additional accurate mass measurements performed using electrospray tandem mass spectrometry (data not shown) confirmed the molecular formula proposed for these ions in Scheme 2 and the fact that these fragmentation processes were not laser induced dissociation. The different fragmentation pathways of the precursor ion at m/z 848.6 were summarized in Scheme 2 These results were similar to those obtained by Fournier et al. for PA6 and PA12 dissociation by MALDI-TOF-MS using post-source decay (PSD) [1]. However,

in our case, additional products due to the particular end-group, containing a labile moiety (TFA), were also detected. 3.2. MS/MS study of Polymers 2 and 3 Fig. 3 shows the MALDI-TOF/TOF-MS spectrum obtained for the protonated 3-mer ion [P23 +H]+ at m/z 846.7, selected as precursor ion and activated by laser induced dissociation (LID). In the case of DEPDA-derivatized polymers, numerous product ions characteristic of the DEPDA moiety were observed. Indeed, the dissociation of the ␻ end-group of the precursor ion with charge retention onto the DEPDA nitrogen atom gave m/z 131.2, 114.2, 100.2 and m/z 86.2 product ions. Besides, when the dissociation of the precursor ion involved the neutral loss of the diethylamine (DEA) molecule (m = 73.1 Da) and the retention of the charge onto the polymer moiety, an abundant product ion at m/z 773.6 was detected. These different product ions allow the full structural characterization of ␻ end-group (Scheme 3). The dissociation of the amide bonds of the precursor ion led to the y2  , y1  and y0  ions, observed at m/z 497.5, 314.4 and 131.2, respectively. This ion series permitted us to confirm the mass of both end-groups. As expected, the bn ion series were not observed because the charge was preferentially located on the basic DEPDA end-group favoring the formation of y2  and y1  ions. y3  -DEA ,

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Fig. 3. MALDI-TOF/TOF-MS spectrum of protonated [P23 +H]+ at m/z 846.7. Gray areas correspond to metastable ions.

y2  -DEA and y1  -DEA ions were detected at m/z 607.4, 424.5 and 241.4. They correspond to the loss of a diethylamine molecule from yn  ions. Most likely, the absence of bn product ions, suggested that the yn  -DEA species are produced through the consecutive

decomposition of the yn  ions rather than from the [P23 +H–DEA]+ ion. Moreover, a consecutive loss of a NH3 molecule from yn-DEA  ions led to z2-DEA and z1-DEA ions, detected at m/z 407.4 and 224.3 respectively. The absence of zn ion series, corresponding to a

Scheme 3. Fragmentation pathways of protonated 3-mer [P23 +H]+ ion at m/z 846.7.

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consecutive loss of a NH3 molecule from yn  ions, could indicate that diethylamine loss is kinetically favored compared to the loss of a NH3 molecule or that yn-DEA  ions came from the ion at m/z 773.6. Another competitive loss was observed from yn  -DEA with the loss of propenamine molecule (m = 57 Da) to give j2 and j1 ions, detected at m/z 367.4 and 184.3 respectively. These ions could also come from the direct dissociation of yn  ions. Moreover, they could consecutively lose a H2 O or NH3 molecule yielding to ions at m/z 349.4 (j2 -H2 O), 166.3 (j1 -H2 O), 350.4 (j2 -NH3 ) and 165.2 (j1 -NH3 ). A propenamine molecule from z2-DEA and z1-DEA ion could also explain the ions at m/z 350.4 and 165.2. Therefore, the chemical modification involving the addition of a basic function on ␻ end group allows to fix the charge and promote the formation of yn  ion series rather than bn after the dissociation of amide bond. Indeed, all the product ions observed for Polymer 2 came from consecutive fragmentation of yn  ion via charge driven fragmentation from ␻ end group. The full dissociation pathways were described in Scheme 3. Moreover, unusual ions were detected at m/z 123.2, 183.2, 202.3, 284.3, 285.3 and 366.4. They can be produced through high-energy processes, sometimes observed after MALDI ionization [24]. Probably because of the presence of the basic function on ␻ end group, Polymer 3 gave product ions similar to Polymer 2. However, the similar fragmentation observed could also be due to the relatively large selection window of the time ion gate (±m/z 6) for MS/MS experiments. Indeed, protonated adducts of Polymer 3 [P3n +H]+ and sodiated adducts of Polymer 2 [P2n +Na]+ could be selected together. Moreover, the presence of the same unidentified ions for the both polymers could indicate that these ions came from the ␻ end-group rearrangement, but additional experiments (MS/MS and/or accurate mass measurements) are needed to achieve their characterization. 4. Conclusion To conclude, the first derivatization strategy, based on the addition of a TFA molecule on the ␣ end group (Polymer 1), yielded mainly complementary bn and yn  product ions. This fragmentation, similar to those obtained for peptides or other PA,[1] allows only end groups weight, m␣ and m␻ , to be confirmed. In addition, the neutral loss of a TFA molecule, as well as rearrangement reactions induced by this group, were observed. A second derivatization strategy, based on the addition of a DEA molecule on the ␻ end group (Polymer 2) was also proposed. The basic properties of DEA allow fixing the charge on this group and directing the fragmentation pattern. In this case, the full characterization of ␻ end group structure was obtained. Moreover, yn and consecutive product ions were observed, allowing the determination of m␣ . Rearrangements,

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probably due to DEA group, were also detected. Additional experiments were currently done to elucidate these particular product ions. Finally, whereas the second strategy was more complicated to implement, the addition of a basic function on the end group permits to direct favorably the fragmentation pathways of the polymer, allowing a better structural characterization. Acknowledgments This work has been partially supported by INSA Rouen, Rouen University, CNRS, EFRD, the Agence Nationale de la Recherche (GREEN COATING Project) and Labex SynOrg (ANR-11-LABX-0029). References [1] I. Fournier, A. Marie, D. Lesage, G. Bolbach, F. Fournier, J.C. Tabet, Rapid Commun. Mass Spectrom. 16 (2002) 696–704. [2] M.N. N’Negue Mintsa, L. Lecamp, C. Bunel, Eur. Polym. J. 45 (2009) 2043–2052. [3] H. Mutlu, M.A.R. Meier, Macromol. Chem. Phys. 210 (2009) 1019–1025. [4] F. Pardal, S. Salhi, B. Rousseau, M. Tessier, S. Claude, A. Fradet, Macromol. Chem. Phys. 209 (2008) 64–74. [5] F. Stempfle, D. Quinzler, I. Heckler, S. Mecking, Macromolecules 44 (2011) 4159–4166. [6] G. Montaudo, M.S. Montaudo, F. Samperi, in: G. Montaudo, R.P. Lattimer (Eds.), Mass Spectrometry of Polymers, CRC Press, New York, 2002, pp. 419–522. [7] H. Pasch, W. Schrepp, MALDI-TOF Mass Spectrometry of Synthetic Polymers, Springer, New York, 2003. [8] G. Montaudo, F. Samperi, M.S. Montaudo, Prog. Polym. Sci. 31 (2006) 277–357. [9] C. Wesdemiotis, N. Solak, M.J. Polce, D.E. Dabney, K. Chaicharoen, B.C. Katzenmeyer, Mass Spectrom. Rev. 30 (2011) 523–559. [10] G. Montaudo, M.S. Montaudo, C. Puglisi, F. Samperi, J. Polym. Sci. Part A 34 (1996) 439–447. [11] H. Choi, E.K. Choe, E.K. Yang, S. Jang, C.R. Park, Bull. Korean Chem. Soc. 28 (2007) 2354–2358. [12] F. Samperi, M.S. Montaudo, C. Puglisi, S. Di Giorgi, G. Montaudo, Macromolecules 37 (2004) 6449–6459. [13] A.A. Caouthar, A. Loupy, M. Bortolussi, J.C. Blais, L. Dubreucq, A. Meddour, J. Polym. Sci. Part A 43 (2005) 6480–6491. [14] S.M. Weidner, U. Just, W. Wittke, F. Rittig, F. Gruber, J.F. Friedrich, Int. J. Mass Spectrom. 238 (2004) 235–244. [15] R. Skelton, F. Dubois, R. Zenobi, Anal. Chem. 72 (2000) 1707–1710. [16] S. Trimpin, A. Rouhanipour, R. Az, H.J. Räder, K. Müllen, Rapid Commun. Mass Spectrom. 15 (2001) 1364–1373. [17] A.P. Gies, W.K. Nonidez, M. Anthamatten, R.C. Cook, J.W. Mays, Rapid Commun. Mass Spectrom. 16 (2002) 1903–1910. [18] C. Barrere, M. Hubert-Roux, C.M. Lange, M. Rejaibi, N. Kebir, N. Desilles, L. Lecamp, F. Burel, C. Loutelier-Bourhis, Rapid Commun. Mass Spectrom. 26 (2012) 1347–1354. [19] G. Yuan, F.L. Tang, C.J. Zhu, Y. Liu, Y.F. Zhao, Rapid Commun. Mass Spectrom. 17 (2003) 2015–2018. [20] P. Roepstorff, J. Fohlman, Biomed. Mass Spectrom. 11 (1984) 601. [21] D. F˘arcas¸iu, G. Marino, C.S. Hsu, J. Org. Chem. 59 (1994) 163–168. [22] K. Biemann, Methods Enzymol. 193 (1990) 886–887. [23] B. Paizs, S. Suhai, Mass Spectrom. Rev. 24 (2005) 508–548. [24] M. Macht, A. Asperger, S.O. Deininger, Rapid Commun. Mass Spectrom. 18 (2004) 2093–2105.

Tandem mass spectrometry of low solubility polyamides.

The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. ...
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